Thrombocythemia

In thrombocythemia, too many platelets are produced. Excessive clotting or bleeding may result.

Thrombocythemia usually develops between the ages of 50 and 70. This rare disorder is more common among women.

In the bone marrow, the cells that become platelets increase in number (proliferate). Why the cells proliferate is unknown. But the result is too many platelets. If there are too many platelets, blood clots can form spontaneously. Clots may block blood vessels, especially small ones. Sometimes in thrombocythemia, platelets do not function normally. Then, excessive bleeding may occur.

Causes

Usually, no cause can be identified. This form is called primary (essential) thrombocythemia. Sometimes thrombocythemia is a reaction to another disorder or condition. This form is called secondary thrombocythemia. For example, too many platelets may be produced during an infection, after surgery or chemotherapy, or in response to excessive bleeding or tissue damage, which can occur during a heart attack. Other disorders that can cause thrombocythemia include iron deficiency anemia, cancer that has spread (metastasized), leukemia, lymphoma, polycythemia vera, and rheumatoid arthritis.

Symptoms

Most people do not have symptoms. About one third of people have symptoms due to blockages in small blood vessels. The hands and feet may tingle or feel as if they are burning. The fingertips may feel cold. Sometimes the legs become painful and red because clots block veins near the surface of the legs (a disorder called superficial thrombophlebitis). Vision may be distorted. Other symptoms include headaches, weakness, and dizziness.

Less commonly, symptoms result from blockages in larger blood vessels, including crucial blood vessels. People who also have another disorder such as atherosclerosis are more likely to have a blockage in a crucial blood vessel.

Occasionally, the abdomen swells if too many platelets accumulate in the spleen, causing it to enlarge, or if blood clots cause the liver to enlarge.

If bleeding occurs, it is usually mild. Some people have nosebleeds, or the gums bleed slightly. Some people bruise easily. In a few people, usually those who are taking aspirin or another nonsteroidal anti-inflammatory drug (NSAID), bleeding occurs in the digestive tract.

Diagnosis

Thrombocythemia is usually diagnosed when a routine blood test detects too many platelets. In essential thrombocythemia, the platelet count is usually 2 to 4 times higher than normal.

Doctors must determine whether thrombocythemia is caused by another disorder. Blood tests can help. Sometimes a bone marrow biopsy is necessary. A sample of bone marrow is removed and examined under a microscope for characteristic changes caused by disorders that can increase the platelet count.

Treatment and Outlook

Aspirin and similar drugs such as clopidogrel or dipyridamole are sometimes recommended, because they help control symptoms such as headache and burning or tingling in the hands and feet. These drugs make platelets less likely to stick together and blood clots less likely to form. However, they increase the risk of bleeding.

A drug that suppresses platelet production is occasionally used. These drugs include the chemotherapy drug hydroxyurea, anagrelide (a drug that specifically suppresses platelet production), and interferon-alpha (a drug that affects the immune system). Treatment is typically started when the platelet count becomes very high or when bleeding or clotting problems occur. The dose is adjusted so that the platelet count decreases to a number that is unlikely to increase the risk of clotting. The dose is decreased if the platelet count decreases too much or if the red and white blood cell count decreases. These drugs also suppress production of other blood cells. Because hydroxyurea may increase the risk of leukemia, anagrelide and interferon-alpha may be preferred. These drugs may have side effects, but most older people tolerate the drugs fairly well.

If a drug does not slow platelet production quickly enough, plateletpheresis may be done. In this procedure, blood is withdrawn from one arm into a tube attached to a blood cell separator machine. The machine removes the platelets, then returns the blood minus the platelets through a tube attached to the other arm.

If thrombocythemia is due to another disorder, that disorder is treated. If treatment is effective, the platelet count usually returns to normal.

Thrombocythemia is usually not life threatening. However, older people are more likely to have a blockage in a crucial blood vessel. Occasionally, primary thrombocythemia changes into a more serious disorder, such as polycythemia vera or certain types of leukemia.